5 rubber stamps cost $9.40. Which equation would help determine the cost of 10 rubber stamps?
Explanation: There are several equations that could help determine the cost, each with a slightly different approach. We know the cost of 5 rubber stamps. We want to know the cost of 10 rubber stamps. We can write the numbers of rubber stamps as a proportion: $\dfrac{5}{10}$ We know 5 rubber stamps costs $9.40. We can let $x$ represent the unknown cost of 10 rubber stamps. The proportion of these costs can be expressed as: $\dfrac{\$9.40}{x}$ The cost changes along with the number of rubber stamps purchased, and so the two proportions are equivalent. $\dfrac{5}{10} = \dfrac{\$9.40}{x}$